Web pages can display information, including articles, images, search results, and/or advertisements (or “ads”). In some examples, websites participate in ad networks that provide ads to be shown on the websites. Publishers of the websites receive credits or payments from the ad networks when visitors to the websites click on the ads or otherwise act on the ads, such as by purchasing products or services being advertised. The percentage of unique visitors who take a desired action upon visiting a website is sometimes referred to as a conversion rate. For example, the desired action may be filling out a form, visiting a predetermined page, completing a transaction or a purchase, downloading a document, or some other measurable action. A number of factors may affect the conversion rate of a website, such as the layout of web pages, placement of content, ads, and navigation elements, and selection of colors, contrast, fonts, and font-sizes. Some websites with web pages that are more attractive to viewers and easier to navigate may have higher conversion rates than websites having cluttered and unattractive web pages.
A publisher of a website may experiment with different configurations of the website using, e.g., A/B testing or multivariate testing. In a conventional A/B testing, two versions of the website that differ in one parameter are displayed to viewers, and statistics on the two versions are gathered and compared. In multivariate testing, multiple parameters are tested simultaneously. By comparing the results of various configurations of the websites, the publisher can determine which configuration may result in the highest conversion rate, leading to the highest ad revenue.